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Radio Galaxies – Narrow Line – Broad Line • Seyfert – Type 1 – Type 2

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Optical View: Type I AGN: Q2130-431 Q2130-431 Broad permitted lines Strong & variable continuum Type II AGN: Q2125-431 Q2125-431 Narrow forbidden & permitted lines Weak & constant continuum [Fig. from Hawkins 2004] Unification Model AGN intrinsically the same: Basic Ingredients mass *Supermassive BH *Accretion disk + corona *BLR: high velocity, high density gas on pc scales *NLR; lower velocity, lower density gas on kpc scales *Torus: gaseous & molecular absorbing medium in equatorial plane embedding BH, ADC, BLR *Jets: relativistic ejection (10% AGN) Differences ascribed to viewing angle: Type I Type II Spectropolarimetry Measure of polarization of light as a function of wavelengths Instrumental in the development of Unification Model: Detection of broad permitted lines in polarized light in Sy2 NGC 1068 (Miller & Antonucci 1983) : * presence of hidden BLR (HBLR) * constraints on location and geometry of the absorber But exceptions exist: *Only 50% of Sy2 have HBLR (e.g. Tran 2001) based on 3-m (Lick) and 5-m (Palomar) telescopes * Result confirmed by Keck 10-m telescope (Moran et al. 2007) • Blazars – BL Lacs – OVV • Quasars – Radio Loud – Radio Quiet • Radio Galaxies – Narrow Line – Broad Line • Seyfert – Type 1 – Type 2 .Low Ionization Nuclear Emission-Line Regions (LINERS) Radio galaxies associated to Elliptical galaxies Radiation power in radio area exceed the radiation power in the visual spectral area Radio galaxy They could be identified among other dimly objects in the visible light, because... − The galaxy in the visible light is not outshined by its core nearest radio galaxy: Centaurus A (NGC 5128) Radio Sources • Only few % of galaxies contain AGN • At low luminosities => radio galaxies • Radio galaxies have powerful radio emission - usually found in ellipticals • RG 10 38 - 10 43 erg/s = 10 31 - 1036 J/s • Quasars 10 43 - 10 47 erg/s = 10 36 - 10 40 J/s 8 R Radio Galaxies Optical image Radio image Centaurus A (“Cen A”): the most nearby AGN (3 - 4 Mpc). .There is strong evidence that Centaurus A is a merger of an elliptical with a spiral galaxy, since elliptical galaxies would not have had enough dust and gas to form the young, blue stars seen along the edges of the dust lane. Radio Galaxies Optical jet Optical image Radio image M 87: The central galaxy (giant elliptical galaxy) of the Virgo cluster of galaxies at a distance of 16 Mpc (redshift z=0.00436) Radio radiation The radio emission is synchroton radiation (emitted from electrons gyrating along magnetic field lines) The most common large-scale structures are called lobes: these are double, often fairly symmetrical structures placed on either side of the active nucleus. In 1974, radio sources were divided by Fanaroff and Riley into two classes, now known as Fanaroff and Riley Class I (FRI), and Class II (FRII). FRI FRII A prototypical radio galaxy Lobes Core Hot-spots Jets . Any size: from pc to Mpc . First order similar radio morphology (but differences depending on radio power, optical luminosity & orientation) 23 28 . Typical radio power 10 to 10 W/Hz Radio Galaxies and Jets Cygnus-A → VLA radio image at -ν = 1.4.109 Hz (d = 190 MPc) 150 kPc Radio Lobes ← 3C 236 Westerbork radio image ν 8 Radio Lobes at = 6.08.10 Hz – a radio galaxy of very large extent (d = 490 MPc) 5.7 MPc Jets, emanating from a central highly active galaxy, are due to relativistic electrons that fill the lobes 19 Cen A as an active galaxy is usually classified as a . FR I type radio galaxy, . as a Seyfert 2 object in the optical (Dermer & Gehrels 1995), . and as a "misdirected" BL Lac type AGN at higher energies (Morganti et al. 1992). It is one of the best examples of a radio-loud AGN viewed from the side ( ~ 70 degree) of the jet axis ( Graham 1979; Dufour et al. 1979; Jones et al. 1996). Jets: Focussed Streams of Ionized Gas lobe jet energy carried out along channels material flows back towards hot galaxy spot 21 A prototypical radio galaxy bowshock undisturbed intergalactic gas backflow splash-point “cocoon” shocked jet gas What makes the difference? Well known dichotomy: low vs high power radio galaxies Differences not only in the radio WHY? high-power radio galaxy low-power Intrinsic differences in the radio galaxy nuclear regions? Accretion occurring at low rate and/or radiative efficiency? No thick tori? The Fanaroff-Riley Dichotomy Is the dichotomy • Environmental? • Interaction of the jet with ambient medium either causes the jet to decelerate (FRI) or propagate supersonically to large distances (FRII) • Intrinsic? • Properties of the central engine govern large-scale morphology (FRI/FRII) Radio Galaxies •Emit most of their energy at radio wavelengths •Emission lines from many ionization states •Nucleus does not dominate galaxy’s emission •Host galaxies are Elliptical/S0 Radio morphology first classified by Fanaroff & Riley (1974) •FR I: less luminous, 2-sided jets brightest closest to core and dominate over radio lobes •FR II: more luminous, edge-brightened radio lobes dominate over 1-sided jet (due to Doppler boosting of approaching jet and deboosting of receding jet) Spectroscopic classification of radio galaxies •NLRGs (Narrow line …): like Seyfert 2s; FR I or II •BLRGs (Broad line …): like Seyfert 1s; FR II only Different types of AGNs: a summary Optical Emission Line Properties Type2 Type 1 Type 0 narrow line broad line Radio quiet Seyfert 2 Seyfert 1 ? Quasars Broad absorption line QSO Radio loud low power BL Lac Narrow-line OVV radio galaxies high power broad-line RG lobe/core dominated QSR Decreasing angle to line of sight Radio galaxies.: These objects can broadly be divided into low-excitation (WLRG) and high-excitation classes (Hine & Longair 1979; Laing et al. 1994). Low-excitation objects show no broad but also no strong-narrow emission lines, and the emission lines they do have (only weak narrow lines) may be excited by a different mechanism (Baum, Zirbel & O'Dea 1995). Their optical and X-ray nuclear emission is consistent with originating purely in a jet (Chiaberge, Capetti & Celotti 2002; Hardcastle, Evans & Croston 2006). They may be the best current candidates for AGN with radiatively inefficient accretion. High-excitation classes By contrast, high-excitation objects (narrow-line radio galaxies) have emission-line spectra similar to those of Seyfert 2s. The small class of broad-line radio galaxies, which show relatively strong nuclear optical continuum emission (Grandi & Osterbrock 1978) probably includes some objects that are simply low-luminosity radio-loud quasars. The host galaxies of radio galaxies, whatever their emission-line type, are essentially always ellipticals. http://www.vlti.org/events/assets/3/documents/torun2c.pdf Low- and High-Excitation Radio Galaxies Based on strength of high-excitation lines , e.g., [OIII] (Laing et al. 1994) • FRIs are almost entirely • Encompass all NLRGs low-excitation and BLRGs • Significant population of • Almost entirely FRIIs low-excitation FRIIs at 0.1<z<0.5 On small scales (< 15 kpc): 3 types of sources Compact, Flat Spectrum (CFS) usually < 1”, physically small < 10 pc -α fν~ν , α~0 – 0.3 variable, polarized, superluminal on VLBI scales Compact, steep spectrum (CSS) alpha = 0.7 – 1.2 sizes 1-20 kpc (within host galaxy) peak at < 500 MHz (limited by Ionospheric cutoff is at 10 MHz) 30% of cm-selected radio sources GigaHertz Peaked Spectrum (GPS) radio spectrum peaks at 500 MHz to 10 GHz sizes < 1 kpc (within NLR) not very polarized alpha ~0.77 for E>E(peak) 10% of cm-selected radio sources Bicknell + 1997 ApJ 485, 112 Spectral shape and Lifetimes Radio sources “age” spectrum steepens Energy loss from radiation, adiabatic expansion 1/2 −1/2 Electron lifetime × 4 B [ ] t≃ 2. 6 10 2 2 1+ z ν b yr B + BR Break freq. Equivalent magnetic field of the microwave background Van der Laan & Perola 1969 GPS: B=10-3 G, nu_b=100 GHz t=2000 years 100 Mhz t=70,000 years CSS: B=10-4 G, nu_b=100 GHz t=70,000 years 100 MHz t=2 million years “Compact Steep Spectrum” Radio Galaxies • small radio sources (<1kpc) with steep spectral index: really small (no shortened by projection effects!) • Morphologically similar to kpc-Mpc double-sided radio galaxies (i.e. they have mini-lobes and/or jets on scales 1pc – 1kpc). The centre of activity, the “core” has an inverted radio spectrum and does not dominate the radio emission at cm wavelengths They are considered to be newly-born radio galaxies CSS Compact steep spectrum sources (=CSS) − ≤1“ in size, steep spectrum , peak at ca. ≤100 MHz – not visible − CSS sources are 10000-100.000 years old CFS − Compact flat spectrum (=CFS) GPS Gigahertz peaked spectrum sources (=GPS) − Spectrum with convex form, peaks at ca. 1 Ghz − High frequency peakers (HFP) Like GPS, peak at >5 Ghz GPS galaxies are young radio sources (~100- 1000 years old) CSS (compact steep spectrum) CFS (compact flat spectrum) GPS (gigahertz peaked spectrum) Different classifications. The same object! • Blazars – BL Lacs – OVV • Quasars – Radio Loud – Radio Quiet • Radio – Narrow Line – Broad Line • Seyfert – Type 1 – Type 2 What do we need to start a radio galaxy? (or how do you make a black-hole active?) o Supermassive BH seem to be common among big early-type galaxies: but only a minority are active. o They need fuel! o Interactions/merger can bring gas to the central regions to feed the monster! Possibility: the AGN-phase (including the radio activity) is only a “short” period in the life of a galaxy. Possibly, every galaxy goes through it. Powerful radio galaxies core dominated lobe dominated broad line narrow line characteristics that are not orientation depended should be similar between powerful radio galaxies and quasars Central Quasars • Radio Quiet Quasars: – Strong emissions in both the optical and X-ray spectrums.
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